Nonhunting angular control system



Sept. l2, 1939.

A. S. RIGGS NONHUNTING ANGULAR CONTROL SYSTSI Filed Oct. l2, 1936 .'5 Sheets-Sheet l IN VEN TOR.

. B gkff nom/ EY Sept. l2, 1939.

A. s. RIGGs 2,172,410

NONHUNTING ANGULAR CONTROL SYSTEI Filed Oct. 12, 1956 3 Sheets-Sheet 2 ATTORNEY Sept. 12, 1939. A. s. Rises NGNHUNTING ANGULAR CONTROL SYSTEI 5 Sheets-Sheet Filed Oct. l2, 1936 7 f ww @A 57./ R my m 1 N Patented sepa 12, 1939 PATENT OFFICE NONHUNTING ANGIIILAII` CONTROL SYSTEM v Alger S. Biggs, Washington, D. C., assignor of one-third to John B. Brady, Washington, D. C.

Application October 12, 1936, Serial No. 105,349

a claims. (ci 11s-23s) My invention relates broadly to angular position control systems such as are employed for the remote positioning of searchlights, guns, steering gear mechanism, and thelike, from a directing or transmitting station remote from the object to be controlled, and more particularly to an improved system of remote control having a. high degreefof accuracy.-

One of the objects of my invention is to provide an apparatus, method of control, and circuit arrangement therefor, whereby high degrees of accuracyv may bepbtained in a remote angular positional control system substantially free of detrimental eiects of hunting.

Another object of my invention is the provision of apparatus and`methodsoi utilizing such apparatus whereby high degrees of accllmcy and freedom from dynamic hunting, commonly referred to as surging,may be secured in a remote angum lar positional control system with simple and easily adjusted apparatus.

Still another object of my invention is the provision of means in a remote electrical angular positional control' system for obtaining a control signal for the follow-upmotor which assists in bringing the controlled load up to correct speed when thel displacement between transmitted di- Y rection and controlled object is increasing, while also providing means for a control signal com- 30' ponent which assists in bringingthe load to a quick stop when the displacement between transmitted direction and controlled object is decreasing. v v

A further "object of myinvention is the pro- 35 vision of circuits and apparatus by which the various component parts of the control signal actuatingl a remote angular positional controlv system may be independently adjusted 'to meet varying conditions of inertia and resistance o loading on the controlled object.

These. and other objects of my invention will be manifest from the following speciilcation and the appended claims 'together with the accompanying drawings in which:

45 Figure 1 is an elevational view of two component parts of a remote angular positional control system arranged on' av common; base in accordance with my invention and coupled together in accordance with and through apparatus form- 5'0 ing a part of my present invention; Fig. 2 is a --vertical sectional view partially in side elevation of the apparatus shown in Fig. l, in which the essential features of one form of coupling device my invention are illustrated; ll'ig.- 3 is ggc'iancnronmseggomivlewmnonunes-:c:

Fig. 2 showing a transverse .section through the coupling apparatus forming a part of my invention; Fig. 4 is alongitudinal sectional view of a Selsyn type repeater motor utilized in one circuit embodying my present invention and shown 5 as built into a unit with an electro-magnetic damping device similar generally to the coupling device shown in detail in Figs. 1-2-3; Fig, 5 is transverse sectional view taken on line 5-5 of Fig. 4 which illustrates the construction of the 10 damping device; Fig. 6 illustrates a complete angular positional control system constructed according to my present invention and utilizing as a component part the apparatus shown in detail in Figs. l-2 and 3; Fig. 7 is a complete angular 15 positional control system constructed according to my invention and utilizing as a'component part the apparatus shown in detail in Figs. 4 and 5; and Fig. 7a. shows a modiilcation of a portion of Fig. '1, 20

In electrical remote positioning control systems, in which a. heavy object is angularly controlled from a. Selsyn type data transmitter, it is essential that the load or controlled object be made to faithfully follow the movements of the transmitter without overshooting the coincidence point. Also it is essential that the object be made to follow with great accuracy the angular direction of the transmitter during periods of high acceleration.

Heretoiore numerous circuits have been utilized in an e'ort to eiectively control the inertia of the controlled object in a manner calculated to prevent the detrimental eiects of hunting and overshooting, and while such circuits have been eiective to some degree, the apparatus and methodsv employed have generally been of complex and delicate nature, requiring frequent ad'- justment for changes in load conditions of the controlled object. 40

My present invention provides means for producing a dead beat or non-hunting follow-up control system possessing high degrees of accuracy and stability while at the same time employing simple and effective methods of obtaining permanent adjustment.

Referring to Figs, 1, 2 and 3 in detail, the Selsyn" typel receiving devices R and RR are mounted on a common base i by the supporting lbrackets 2 and 4 and secured by suitable means 50 such as bolts shown at t-i-a-lna. 'I'he top receiver R. is adapted to be driven by the followup system thiough the gear 25 and through the coupling II-iZ-ila and 30, while the lower receiver is dynamically coupled to the other receiver through the electromagnetic drag device C The device C consists of the outer core l5 secured by suitable means to the end bell i8, an extension 22a, of `which servesto support the entire mechanism in the bracket 6 and to carry the driving gear 25. A shoulder 22 serves to position the inner race of the free ball bearing 23, while the spacer 24, gear 25, spacer 26, inner race of bearing 2'! are all locked on the extension 22a of the end bell i8 by the thread lock rings 2li-29 forming a complete unit. The rings 34-35 attached to the bracket ,6 and the cap 36 by the through bolts 35a serve to retain the outer race of the ball bearing 2l thereby supporting the entire assembly of the device C. The coupling 3@ is keyed to the shaft and has a slot l2a which is engaged by pin l2, carried by arm il for driving the rotor of the receiver R.

The device C has an inner core i6 maintained in position by the bolt 33, spacer 33a and nuts 3|-32. Upon the inner core i6 are wound the iield coils H which are electrically connected (by leads not shown) to the slip rings lil- 20 supported on the end bell it and insulated therefrom by the insulating material i l Brushes (not shown on the drawings) serve to convey current to the rings lQ-Zli and hence to the field windings I'I.

The receiver R is supported in the bracket 2 as shown by the hub l being clamped by the cap 8. The receiver may be rotated about its axis for purposes of .adjustment and is locked in a selected position by tightening the bolts of they clamps 8.

Likewise the receiver RR is held by the hub i3 being secured in position by means of clamp i4. The bolts extending through the clamp Elfi and into the bracket insure the rigid support of the receiver RR.

The rotor, of conducting but non-magnetic material, 40 of the device C is attached at 39 to the shaft of 'the receiver RR and is free to rotate in the annular air gaps l5a and 96a separating the main core l5 and the inner core i6. With the eld coils ll'l energized from a suitable source of D. C. power the coupling device C, due to the flux across gap IGa-I'Ia through I the rotor 4U, will tend upon rotation, to revolve the rotor of the receiver RR due tothe heavy eddy currents set up by rotation of the rotor i0 in the flux between the core i5 and the inner core I6. Likewise if the coupling C is not rotating it Will be understood that under like conditions the rotor of the receiver RR is restrained or damped in rotation by the eddy currents induced in the rotor 40.

In other words, the coupling device C provides coupling between the driven receiver R (top) and the free receiver RR (bottom) which depends upon their relative rates of rotation.

If either is rotated relative to the other at a high rate the coupling is large tending to oppose lthe movement, lwhile either may freely move relative the other at a very slow rate.

Thus the receiver RR may assume a position corresponding to the angular direction of the transmitter to which it is connected independently of the angular position of the receiver R, but its movement is so damped that it may move only at a very slow rate of speed from one angular position to another.

In Figs'. .1i-5, I have shown a Selsyn type receiver built in a unit with an electromagnetic damping device generally similar to the coupling ateatro device C. The Selsyn receiver comprises the stator and associated coils 4|, the rotor 42 and the end bell 43. The upper end of the stator is attached to the bonnet 44 which holds the outer core 52 of the damping device. End bell 45 is attached to the other end of the core 52, thereby forming a single direct connected unit of the Selsyn receiver and the damping device.` The inner core 46 oi the damping. device with eld coils 5| :is-supported and held with respect to the end bell 45 by the bolt 41, spacer 50 and nuts 48 49. Terminals not shown provide for circuit connections for energizing the eld coils 5| from a suitable source of direct current power.

A rotor 54 (similar to rotor 40 of Fig. 2) is attached to the shaft of the receiver at point 53 so that rotation of the receiver rotor is damped in fashion similar to the damping of the rotor of the receiver RR of Figs. 1-2-3.

The thrust of the rotor of the receiver in Fig. 4 is taken by a ball thrust bearing as shown at 43a, and similarly, though not shown, the rotor of the receiver RR in Figs. 1 2-3 is also supported on a like ball thrust bearing.

In Figs. l-2-3-4-5 certain essential details as brushes and terminal leads are omitted for sake of clarity inasmuch as their arrangements are well known to the art and except diagrammatically are of no importance to an understanding of my invention.

A mechanical damper 42a is shown in Fig. 4, but it is sometimes better to oinit this inasmuch as it adds considerable inertia to the receiver rotor, and its advantage is largely eliminated through the electromagnetic damping of the rotor 54 in the flux of the damper section of the ma.- chine shown in Figs. 4-5 when rotating in the annular air gap 52a and 46a.

Referring now to Fig. 6, I have shown in diagrammatic form a complete angular positional y control system embodying my invention and In this ligure a searchlight |32 is made to follow the angular position of the telescope El.v

The telescope is moved angularly by the hand crank lll through the gears 69-68, shaft 61, gears E56-85, shaft 54, gears 63-62 and shaft 6|. Simultaneously the shaft 61 drives the rotor of the transmitting device A. In accordance with the control system hereinafter described in detail, the motor M through vshaft |25, gears i26--|2'|, shaft |28, gears |29-l30, and shaft |3I control the angular position of the searchlight l32 in agreement with the telescope 60.

The transmitter A comprising the primary winding 1| (here shown on the rotor) supplied at points 13-14 from a suitable source of alternating current power and'short circuited between the points 'l5- 16 to reduce iiux distortion is adapted through its cooperating secondary winding 12 (here shown on the stator) to transmit angular direction to the control system.

The transmitter secondary winding 12 is tapped at points 'l1-'I8-19, thus simulating a three phase winding, and connected through conductors -8I--82 to corresponding points 88-89-90 respectively, of the primary winding L,86 of the receiver R which is adapted to provide the displacement control signal component. The secondary Winding 81 (rotor) of the receiver R is tapped at points 9|-92 and connected through winding 91 of the displacement signal transform- Y nected to the stator winding |04 of the receiving Y as device RR through conductors 8l'-8|"02' to points III-IlI- lll 'I'he rotor winding |05 of this receiving device is tapped at points IIIB-Iil-III and so connected to the transformer H and the source of power energizing the transmitter A that the rotor and stator of thereceiving device RR operate as a standard Selsyn type repeater in following the angular position of stator and rotor of the transmitter A, and in addition, provide a voltage acro the primary winding lil of the "rate signal transformer H due to relative displacement of the rotor winding |05 and the flux in the stator produced by the currents in the stator windings ill. This double function o f the receiving device RR may be best understood by considering it only in relation to the transmitter A. Y

It will be seen that the transmitter A and the receiving device RR are fundamentally equivalent to a conventional Selsyn type transmitter and receiver, the rotor |05 of the receiving device RR being "polarized on the vertical axis corresponding to point and a point midway between points IIO-I through power supplied at point |09 and the center tap'l Il of the primary winding il! of the transformer H. Now when the roftors of transmitter A and device RR are in exact angular agreement there is no voltage present across the primary winding H2 of the transformer H since this winding is connected at its outer terminals to the rotor winding at points I |0-I I, which are 90 inductively from the normal flux axis in the device RR. However upon relative movement of rotor winding and stator flux, a voltage-exists across points IIB-I and hence acrossV the primary winding I|2 of the transformer H.

Normally the rotor of the device RR is free to establish the equilibrium position with the transmitter A, under the retarding or damping action of the magnetic coupling device C. Therefore, under any steady state condition the rotor of the device RR is in agreement with the rotor of the transmitter A, and no voltage is present at the primary winding ||2 of the transformer H.

The coupling device C (described in detail in reference to Figs. 1, 2 and 3) tends to opposed relative motion of the rotors of the receiver R and the device RR in proportion to the rate of the movement. hence a rapid movement of the rotor f of device R results in a'strong torque tending to produce a like movement in device RR. Likewise a quick movement of the rotor of device RRre-v sulting from its own internal torque is opposed by the coupling device C.

' The static condensers 03-40-05 serve to supply a portion of the wattless magnetizing currents taken by the receiving control system, thus preventing overloading of the transmitter A as shown in my copending application Serial No. 101,529, filed September 18, 1936.

Supposenowthatthe entiresystemisenergized, and that telescope 00 and light |32 are in exactangularagreement asshowninFlg. 6. The ampliner AA is supplied at points lll- |20 with power. andin accordance with inputzsisnals at the terminals H-ill controls the direction and speed of the motor M having a field winding l2 and its armature |22 connected to the amplifier, output terminals. Any conventional form. of amplifier may be employed such as shown in Arnold Patent 1,403,475, dated January 17, 1922;

Mathes 1,426,754, dated August 22, 1922; or

Mathes 1,493,217, dated May 6, 1924. (I have not shown the details of the amplifier AA, which may be either of the electron tube type, or of "lo tubeless construction, inasmuch as 'the ampliiler construction does not form an essential part of the invention disclosed and claimed in this case).

The secondaries 90| l5 of the transformers G and H are connected together at their terminals ||8||1 respectively, and through adjustable taps 99||0 to the input of the amplifier AA.

Under the above condition (exact angular agreement) the input `voltage at terminals |00i0| of the ampliiier AA is zero, since the 2 magnetic axis of rotor winding 81 of the receiver R is at 90 from the flux producedl by its stator winding 86, also the magnetic axis corresponding to points ||0||| of the device RR is at 90 to u sponding displacement existsV in the stator flux 3 of the receiver R, and its secondary windingll is now inductively coupled to its primary flux hence a voltage is present across the transformer G corresponding to the sine of the angle of transmitter displacement. the device RR has been shifted clockwise and the magnetic axis of points ||0| II is now inductively coupled to the flux produced by the combined magnetomotive forces of the rotor polarizing current and the stator currents. As a result of this condition a voltage exists across points ||0||| and hence across transformer H corresponding to the sine of the resultant angle of field displacement in device RR, also a.v

torque is produced in the device RR tending to rotate 'its rotor to a position 3 clockwise from that shown.

Now the voltages across transformers G and H are combined in such polarity that they add under the conditions above stated. The result is that the net voltage input to the amplifier AA at-points |00|0| is the sum of that produced in the receiver R and that produced in the device RR. The internaltorque of the device RR, however, rotates its rotor (under restraint of the coupling device C) to agreement with the transmitter, therefore reducing the voltage acrom points ||0||| to zero. Thus after a short interval of time the input voltage 'at the amplifier drops to that produced in device R.

If now the motor M is released the torque resulting from the amplifier output will drive the searchlight in a direction to rotate the rotor of the device R into agreement with the transmitter, or clockwise 3. Simultaneously, how- 05 ever, with the movement of the rotor of device R, the coupling device C through magnetic linkage between its stator" |5|0 and its rotor" l0 drags the rotor of the device RR in a clockwise direction, thus establishing acres points msothenuxm mitter. VThis differential action of the voltage produced in the receiver R and the device RR introduces into the ampliiier a control signal which is dependent upon the relative displacement between telescope 60 andl light |32 plus or minus the rate oi change of relative dlsplacement. 'I'he voltage produced by the device RR therefore provides a higher net signall than that due to relative displacement when the displacement in increasing, thus helping to accelerate the load driven by the motor, and a lower and even a reversed net signal than that due to relative displacement when the displacement. is decreasing, thus assisting in so controlling the motor as to avoid the searchlight overshooting" the coincidence point` with the telescope.

Likewise under a reversing condition when the searchlight is following the angular rotation of the telescope the voltage of the device RR supplements the displacement voltage of the receiver R in such manner as to oppose relative motion between telescope and searchlight, thereby eliminating the effects of dynamic hunting commonly referred to as surging Considerationof the operation of the system of Fig. 6 indicatesthat for any steady state condition; viz:-at rest, or running at constant speed, the relative displacement between the stator and rotor magnetomotive forces of the device RR is zero, and that displacement exists, with resulting voltage across points itil-i it only when telescope and light are moving relatively to each other.

The taps SS-l |6 on the transformers G and H respectively permit of independent adjustment of sensitivity of control to relative displacement and rate of change ot v'relative displacement between the telescope and' the light.

Further consideration of Fig. 6 indicates that the rotor of the device RR derives its torque from the transmitter independently of the receiver R,

while the rotor of the receiver R is driven synchronously with the light by the follow-up motor.

Thev operation of the'system of Fig. 7 is esl sentially similar to that shownv in Fig. 6, except that the rate voltage is secured by a slightly diiferent'arrangement of apparatus which is in some instances superior to the arrangement of Fig. 6. Corresponding parts are designated alike in Figs. 6 and '1, but where exact counterparts are used in slightly different arrangement they are shown differently in the two figures.

In Fig. 7 the telescope is similarly operated to Fig. 6 and the transmitter A is identical in all respects. The receiving device in Fig. 7 however consists of 'a differential transformer by which relative displacements betweentelescope and searchlight may be conveyed to the control system as angular eld displacements instead of their corresponding voltages.

The transmitter secondary winding is connected at points 11-18-19 through conductors 80-8I-82 to corresponding points |43|44|45 of the primary winding |4| of the diierential transformer B, the rotor of which is driven from amano the motor M by the gears in similar fashion to the drive of the rotor of the receiver R in Fig. 6.

The secondary winding |42 of the differential transformer B is tapped at points |46|41|48 and electrically connected to corresponding points l5i-l52-I53, |59-|60-|6| of the stator windings HQ and |51 of the device E and the device F respectively.

The device E is exactly similar to the device RR of Fig. 6 and is polarized in like manner at points |54 and the center point |11 of the primary winding |16 of the transformer H whose opposite terminals l are connected to points l55|56 corresponding to points llll--l of the device RR of Fig. 6.

The device F is similar to the receiver R of Fig. 6-and its secondary winding |58 is connected at points IGZ- |63 to the primary winding U10 of the transformer G'.

The voltage produced by device E across the primary of transformer H' corresponds to that produced across the transformer H of Fig. 6, `vvhile the voltage produced by the device F across the primary of transformer G corresponds to that produced across the primary of transformer G of Fig. 6.

The rotor of the device F is normally clamped in a xed position so that relative displacement between telescope and searchlight establishes a voltage across its secondary or rotor winding |58. The device F may be dispensed with in some instances, and its function in that instance is simulated by connection of the transformer primary winding i'lll to the secondary terminals MTI-M8 of the device B, as shown in Fig. 1a by conductors iBS-|69. Under this condition the conductors ltd- E65 and the device F are removed, as are the connections to points i59--|6-|6i.

Suppose now that the rotors are positioned as shown, and that the motor is blocked to prevent its rotation. Now let the rotor of the transmitter A be moved clockwise by 3. Immediately a corresponding field displacement is present in the devices E and F, producing corresponding voltages across the primary windings of the ltransformers HG. 'I'he combined voltage is impressed upon the amplifier input terminals |00|0| through the network including adjustable tap |12 on secondary |1|, terminals |13|1, secondary |14a and adjustable tap |15.

Simultaneously with the displacement of the field in device E, a torque is developed therein tending to rotate its rotor to a position where its rotor and stator magnetomotive forces are again on the same plane, but `this movement is opposed by the damping device D in such manner as.. to retard the movement of the rotor of the device E.

The combined voltages of the device E and the device F across the transformer H'-G' respectively, represents a signal having two components as in the system shown in Fig. 6. The voltage of the device F across transformer G being due to relative displacement between light and telescope, and the voltage of the device E across the transformer H' being due to relative rate of change of displacement between telescope and light.

If the motor is released, the amplier output signal drives it in 4.direction to rotate the rotor of the differential transformer B through an angle corresponding to the original transmitter displacement, thereby'ditferentially canceling the displacements from the normal axes of the devices E and F. Simultaneously however with the movement of the rotor of the-differential transformer B inresponse to the input signal of theamplifler, the resulting internal torque of the device E tends to keep its rotor and stator magnetomotive forces in alignment, but the damping or retarding action of the damping unit D results in relative displacement in these magnetomotive forces and resulting voltage across points ISL-|56 of the rotor winding of device E, thereby resulting in the net ampliiier input signal reaching zero, or reversing, before actual coincidence is reached between light and telescope.

The voltage of the device E is therefore of direction and magnitude to oppose relative motion or displacement betweenlight and telescope, while the voltage of device F is of such direction and magnitude as to drive the motor in direction to cancel relative displacement. Fundamentally the systems shown in Figs. 6

land "I are identical, but in Fig. 'l the rate indicated by the`relative displacements between the rotors of the transmitter A and the differential transformer B, but the voltage across the points ISS-|56 and hence across the primary of the transformer H', will be zero except during ychanges of displacement between light and telescope. l

' Although I have shown and described my in'- vention as applied to searchlight azimuth control in accordance with angular directional signals from a distant telescope, and in two representative forms, I do not desire to be limited thereto, inasmuch as my invention is applicable broadly to any control system wherein a heavy object is to be positionally controlled in accordance withangular directions from a Selsyn type data transmitter.

I therefore intend my invention to be limited only to the extent of the appended claims. A What I claim as new and desire to secure by Letters Patent of the United States is as follows: l. In an electrical positional control system a Atransmitter of angular directions, a receiver for producing a signal due to displacement between said transmitter and said receiver, a reversible motor adapted to drive said receiver into angular agreement with said transmitter, a second receiver deriving its positional torque from said transmitter independently of said rst receiver and free to assume an angular alignment with Vsaid transmitter, means for deriving a signal from proportion to rate of said relative movement, an4

amplifier system having its output connected with said motor, and means for impressing the combined -output of both receivers upon said amplifier system for controlling said'motor.

2. In an electrical control system, means ior` establishing a field displacement from a distant point, means for correcting said displacement including a reversible motor, means for establishing a voltage due to said displacement, separate means-for establishing a second voltage due to said displacement, means for cancelling saiddiseither of two points, a reversible electric motor for operating one of said means, means responsive to said displacement for establishing a voltage due to said displacement, a second means for establishing a second voltage due to said displacement, means responsive to said second voltage for cancelling the eii'ects of said displacement on said second means, means for controlling said motor in accordance with both of said voltages, and means for retarding the cancellation of the effect of said displacement on said second means for establishing a second voltage due to said vdisplacement.

4. In an electrical control system, means for establishing aeld displacement from a distant point, means for producing a voltage due to said displacement, a reversible motor adapted through electrical differential means for cancelling said displacement and simultaneously driving a load, means responsive to said displacement for producing simultaneously a voltage, separate from ilrst mentioned voltage, and a torque tending to reduce last said voltage to zero, electromagnetic means of delaying said torque in reducing said last mentioned voltage to zero, and means responsive to both of said voltages for controlling said motor.

5. In combination with a remote transmitter and an object controlled thereby in an electrical positional control system, means for obtaining a voltage proportional to the rate of change -of displacement between the remote transmitter and the object controlled from said transmitter,

, comprising an angular positional 4receiving device connected with said transmitter for deriving its positional control torque from said transmitter independently of said object, electromagnetic eddy current coupling means between said receiving device and said object whereby the change of angular position relative said object is opposed by said coupling means proportional to the rate of change of angular position, and means for obtaining from said angular positional receiving device a voltage ,iiaving direction and magnitude dependent upon its relative displacement from said transmitter 4vi'or vcontrolling the rate of movement of said object in vfollowing said transmitter. 6. Apparatus for controlling an object in angular position-'from a distant point which comprises a transmitter of'angular directions at said distant point, two receiving devices at said object capable of producing voltages Aoi' direction and magnitude dependent upon their angular displacements from said transmitter, means for rotationally positioning one of said receiving devices synchronously with said obiect. means i'or rotationally positioning the other of said receiving devices independently of the aforesaid means butin angular agreement to said transmitter, means including an electromagnetic eddy current damper for opposing relative angular positioning of said receiving devices in'proportion to their rates of change of relative angular position, and means for controlling the first said means in accordance with the relative angular displacements of both of said receiving devices to said transmitter.

7. Means for producing a signal proportional to the angular velocity of a Selsyn type transmitter, comprising a receiver deriving its positional torque from said transmitter, means including an eddy eurent torque motor for causing said receiver to follow said transmitter in angular direction with a disagreement proportional to its speed, and means for deriving from said receiver a signal proportional to said disagreement.

8. Means for compensating for velocity and acceleration lag in an electrical angular positional follow-up control system comprising a separate auxiliary follow-up system including means having inertia characteristics similar generally to those of the main control system, means for deriving a signal from said auxiliary follow-up system, and means for utilizing said signal for differentially controlling said angular positional follow-up control system.

ALGER S. RIGGS. 

